Scientists who hunt for “intelligence genes” used to think there were fewer than half a dozen of them.

Why?

In recent years, they determined there may be at least 1,000 — each with just a tiny effect on the differences in people’s IQ. A study released Tuesday found new evidence that many genes play a role in intelligence, but scientists still couldn’t pinpoint the specific genes involved.

So the whole enterprise is a waste of time?

Many have thought as much. It’s like knowing that somewhere in a big city are 1000 employers who are more likely to give you a job than most.

“It’s been kind of a shock to the system that it hasn’t worked,” said psychologist Eric Turkheimer at the University of Virginia, who had no role in the study. “We can’t find the effects of any individual genes that are large enough to seem worth worrying about.”

They can’t just forget it because too much culture is bound up with notions about IQ, so one suspects they’ll be at it a long time.

To the extent that IQ is governed by genes, the interactions between them and with the environment are critical. Another difficulty for this contentious field is that – within a normal range – there is no systematic relationship between IQ and achievement. That is, a doctor whose IQ is 120 can be just a good a family physician – or better – than a doctor whose IQ is 150. A doctor whose IQ is 175 may not be suited to family practice at all, and could – in that context – be a failure. So the interactions between tested IQ and environment partly depend on the challenges faced.